Synthesis of a novel alkaline-developable photosensitive copolymer based on MMA, MAA, SM, and 2-HEMA-grafted GMA copolymer for an innovative photo-imageable dry-peelable temporary protective plastisol

  • Sheng Chang
  • Jian-He Yang
  • Jung-Hsien Chien
  • Yu-Der Lee
Original Paper

Abstract

Methyl methacrylate, methacrylic acid, styrene and 2-hydroethyl methacrylate were used to synthesize copolymer with carboxylic acid group through free-radical polymerization to develop a prepolymer(PMMSH). Glycidyl methacrylate was then added to react with carboxylic acid groups of PMMSH to form photosensitive copolymer PMMSHgG. Nuclear magnetic resonance and infrared were used to confirm the structures and functional group of the prepolymer and the copolymer while GPC was employed to determine the molecular weight. The sensitivity and resolution of the copolymers were obtained through characteristic exposure curve and SEM observation, respectively. PMMSHgG was also mixed with dry-peelable plastisol, acrylic acid monomer, and photoinitiator to form a photo-imageable dry-peelable plastisol. A suitable peelable composition without scum after UV exposure and post-baking was identified.

Keywords

Dry-peelable plastisol Photo-imageable resist Photosensitive copolymer Polyvinyl chloride (PVC) Free-radical polymerization 

Introduction

Temporary protective coatings are widely used to protect the surfaces of various products, parts, or components during their manufacture, assembly, and shipping [1, 2, 3, 4, 5]. These coatings are used to prevent surface damage such as scratching, staining, and also used to simplify or enhance cleaning operation. A few water soluble examples include water-based polyurethane dispersions [6, 7], water-based vinyl-acrylic and acrylic copolymer emulsions [8]. Those protective films are subsequently removed by dissolution in water. For traditional photo-etching process with negative photoresists for manufacturing indium tin oxide(ITO) touch panel, strong base solution is commonly used to remove the photoresist films after etching process, but this treatment might damage ITO and further decrease the electric conductivity. Therefore, removed protective film simply by physical force (i.e., peeling by hand or adhesive tape) is an attractive strategy to solve the above-mentioned problem. The effective approach is the use of dry-peelable films such as polyvinyl acetate based strippable polymer [9] for radioactive decontamination, waterborne self-crosslinkable sulfourethane-silanol dispersion [10], and poly(vinyl alcohol) film [11]. Dry-peelable plastisol based on polyvinyl chloride [12, 13] which is resistant to high temperature is also a type of temporary protective coating. For example, peelable solder mask [14] is used in the manufacture of PCB when temporary protection is needed on certain areas, especially during high-temperature process, such as hot-air leveling or plating for resistance to strong acid and alkaline. However, all these dry-peelable temporary protective coating cannot protect micro areas. The application scope will be expanded if photoresist [15, 16] resin and peelable plastisol [14] could be combined. This current study described a new photoresist copolymer [17] combined with polyvinyl chloride resin to form a photo-imageable dry-peelabe temporary protective plastisol.

Photoresists play an important role in microminiaturization in the electronic industry [18, 19, 20, 21], such as integrated circuit (IC) photoresist developed for copper wiring process [22] and microcircuits for printed circuit boards [23]. They are also used for the preparation of three primary colors (R, G, and B) and black pixels in color filters of LCD [24, 25, 26]. Negative dry-film photoresist assembly comprises acrylic photosensitive copolymer [27, 28] with carboxylic acid groups, monomer, and photoinitiator. It is covered by negative with images and goes through UV exposure and development with aqueous solution of weak alkali sodium carbonate (Na2CO3). After the plating or etching process and delivery of protection function, the photoresist will be removed via soaking in strong alkali, such as NaOH(aq).

The molecular weight of the copolymer would affect the operability and ability of the developing process. Oligomer (2-hydroxy-ethyl methacrylate-co-cyclohexyl methacrylate-co-isobonyl methacrylate-co-acrylic acid) acquired through free-radical polymerization via chain transfer (Mn = 1,677) was used as the aqueous base developable negative photoresist [29]. Polymer prepared in current study was poly (methyl-methacrylate-co-methacrylic acid-co-styrene-co-2-Hydroethyl methacrylate-grafted-glycidyl methacrylate) (PMMSHgG), which was synthesized through free-radical polymerization but having a large molecular weight. Since photoresist polymer that is subject to contact exposure must have a large molecular weight. The other merit of this polymer is that it is compatible with poly(vinyl chloride), a major component in peelable compositions [30].

In this study, photoresist copolymer(PMMSHgG) was synthesized and mixed with polyvinyl chloride resin, plasticizer, photoinitiator, and acrylate oligomer to form a photoresist formulation. Solid-state membrane was obtained through coating, pre-baking, and removal of solvent. The sample was then covered by a negative with images and went through UV exposure, developed via weak alkaline and post-baking. The process will smelt the polymer, plasticizer, and polyvinyl chloride resin(PVC) to form peelable membrane. In component production, the negative photoresist turned into a tough peelable membrane and had the protective function against scratching, dust, high temperature, strong acid, and strong alkaline. After the temporary protection function was over, the membrane could be peeled through physical method, which would prevent the component from damages by acidic or alkaline chemicals and provide temporary protection on precision areas.

Experimental

Materials

Methyl methacrylate(MMA), methacrylic acid(MAA), styrene, 2-Hydroethyl methacrylate(HEMA) and hydroquinone monomethylether(HQME) were purchased from Showa chemical company. Glycidyl methacrylate(GMA) was obtained from SIGMA. All materials were used as received. Trimethyolopropan triacrylate, dipentaerythritol hexaacrylate, epoxy acrylate oligomer(9,770), aromatic urethane acrylate oligomer(670A2), and diallyl isophthalate prepolymer(DAP) were used as monomers in the resist formulation. PVC POWERS(PR450, PR1069) were provided from Formosa Plastic and PVC resin(H11/59) was purchased from Vinnol.

Measurements

The IR spectra were recorded on a Perkin Elemer 842 spectrometer with a KBr plate. The 1H NMR spectra were recorded on a Bruker MSL 500 MHz NMR spectrometer in d-DMSO. Number-average molecular weight (Mn), weight-average molecular weight (Mw), and polydispersity of copolymer were estimated from gel permeation chromatography (GPC) with TSK columns (AW2500*3) and polystyrene was used as the standard. The acid number in the photosensitive copolymer was analyzed via titration with KOH.

Synthesis of Poly(MMA-co-MAA-co-styrene-co-HEMA)(PMMSH)

The synthesis of PMMSH is illustrated in Scheme 1 and described as follows: A mixed monomer solution was prepared including MMA(38.4 g, 0.384 mol), MAA (11.9 g, 0.138 mol), SM(6.75 g, 0.063 mol) and HEMA(10.15 g, 0.085 mol). Initiator BPO(1 wt%) was added to a four neck reactor with diethylene glycol monoethyl ether acetate (37.31 g) and heated to 80 °C in an oil bath. Nitrogen was fed and the solution was stirred continuously. Droplets of monomer solution were fed gradually in 2 h, and then proceeded the free radical copolymerization for 9 h. As the reaction was completed, the solution was cooled in a water bath. The product was dissolved in THF and droplets of ethyl ether were added to obtain polymer sediments. This process was repeated two to three times. The sediments were placed in a vacuum oven and left overnight to obtain purified PMMSH. The identification of PMMSH including chemical structure, functional groups and acid value were measured by NMR, FTIR and titration, respectively. The compositions of PMMSHs are calculated by NMR spectra and shown in Table 3.
Scheme 1

Synthesis of MMA, MAA, SM, HEMA copolymer (PMMSH)

Synthesis of PMMSHgG

The preparation of PMMSHgG is shown in Scheme 2 [31] and described as follows: Inhibitor HQME (0.92 g) was dissolved in diethylene glycol monoethyl ether acetate, then PMMSH was added. The temperature was increased to 90 °C. GMA (the same molar ratio with MAA, 19.65 g) and catalyst TPP (0.68 g, 1 w%) were added together with diethylene glycol monoethyl ether acetate and the solid content was adjusted to 45 %. The mixture was first cooled in a water bath. Then it was dissolved in THF and droplets of ethyl ether were added to obtain PMMSHgG sediment. This process was repeated three times. The sediment was placed in a vacuum oven and left overnight to obtain purified PMMSHgG. The chemical structure, functional groups and acid value was also characterized by NMR, FTIR and titration, respectively.
Scheme 2

Synthesis of copolymer-g-GMA (PMMSHgG)

Preparation of PMMSH-based and PMMSHgG-based photoresist formulation and lithographic evaluation

A slice of property cut glass substrate, which was washed with pure water, soaked in acetone, placed into supersonic oscillator (15 min), and then wiped with dust-free paper, was used as the substrate. The major ingredients of photoresist were mixed with solvent, cross linking agent, photoinitiator, and leveling agent to the proper ratio of coating, as indicated in Table 1. The clean glass substrate was placed on a spin coater and its center was suctioned with a vacuum pump. After achieving a certain degree of vacuum, the photoresist prepared was applied on 1/3 of the substrate from the center. The coating was then distributed through two stages (first stage: 2,000 rpm for 15 s; second stage: 7,000 rpm for 25 s). The photoresist properly coated glass substrate was placed in an oven for baking (5 min,80 °C) to remove excessive solvent. The sample was taken out for cooling after it had been determined as tackfree. A photo mask was placed on a pre-baked photoresist and exposed through direct contact with an UV light having energy of 4.7 mW/cm2 and full wavelength, thus, the sensitivity and resolution of the photoresist could be obtained by receiving different exposure energy. The image was developed with an aqueous solution of Na2CO3 (1.0 w%) for 10 s and removed the developing solution by washing with DI water. After development, the thickness of residual photoresist membrane on the glass substrate was measured by α-step apparatus (Tencor-P10). The specimen obtained from the microlithography process was also coated with a thin layer of Au through Ion vacuum sputter. The morphology and photoresist resolution of photoresist pattern on the specimen was then observed by a scanning electronic microscope (SEM).
Table 1

Formulation of photoresist

Ingredient

%

PMMSH/PMMSHgG

20

Photoinitiator (Irgacure 907)

5

Monomer (trimethylolpropane triacrylate)

15

Solvent (diethylene glycol monoethyl ether acetate)

58

foam control agent

2

Preparation of PMMSHgG-based photo-imageable dry-peelable plastisol formulation

(A)Lithographic evaluation

The basic formula of photoresist peelable plastisol is described in Table 2. Ethylene glycol monobutyl ether, plasticizer (Dibutyl phthalate, DBP), and acrylate oligomer(670A2) were added into PMMSHgG, stirred thoroughly (10 min), then photoinitiator (Irgacure 907) and stabilizer (soybean epoxy) were added, and the solution was stirred for 5 min. The PVC powder and pigment were added, stirred (10 min), and placed into a three-roller mill for grinding twice. Finally, a foam control agent was added and stirred (5 min) to complete the process. The copper foil laminates were soaked into diluted sulfuric acid (5 w%) solution to remove the oxide scale on the surface of copper coil, washed with distilled water and dried with hot air. The photoresist peelable plastisol was applied to the copper foil laminates via screen printing, left to stand still (3 min), and leveled. The copper foil laminates was placed in a 60 °C oven with hot air circulation (30 min) for pre-baking. The negative with images was placed on pre-baked copper foil laminate and in contact with a exposure device (C SUN MFG Exposure UVE-M720) (the exposure energy is 400 mJ/cm2). After the exposure is completed, the copper foil laminate was placed in a SONGTEC developing machine containing Na2CO3(aq) (1 wt%) for development and imaging. The image resolving ability (photoresist’s line width) was recorded.
Table 2

Formulation of photo-imageable dry-peelable plastisol

Ingredient

%

PMMSHgG

10

PVC

50

Plasticizer(DBP)

12

acrylate oigomer(670A2)

13

Photoinitiator(Irgacure 907)

8

Stabilizer(soybean epoxy)

5

Pigment(blue)

1

foam control agent

1

(B)Physical property tests

A glass substrate with dimension of 20 cm × 30 cm was prepared. It was washed with pure water and wiped with acetone, then dried in a oven with circulation of hot air at 60 °C for 15 min. Photoresist peelable plastisol was prepared with the formulation shown in Table 2. Three different types of PVC powder including PR-450, PR-1069, and H 11/59 were tested. After 10 min of stirring, the sample was placed in a three-roller mill and grinded twice. The dried and cooled glass was then placed on a horizontal coating machine. The photoresist peelable plastisol was coated with a 50 um scraper horizontally then stand still for 3 min. The glass substrate was dried in a oven with the circulation of hot air at 60 °C for 30 min and finally was placed into the exposure machine, vacuumed, and started exposure until the energy accumulated to 400 mJ/cm2. After completing exposure, the glass substrate was placed into a oven with circulation of hot air (130 °C) for 30 min. After cooling, the membrane was peeled directly and was observed whether it could be peeled completely, thus, a peeling test and tensile damage test were conducted.

Results and discussion

Synthesis and characterization of PMMSH

Purified PMMSH was dissolved in d6-DMSO and 1H-NMR was used to verify its structure and characteristic peaks, as shown in Fig. 1. Chemical shift δ = 1 ~ 2 ppm was generated by CH2 on the main chain and CH3 on the side chain. The correct copolymerization ratio of MMA-MAA-SM-HEMA was unknown and the characteristic peak of each ingredient must be obtained to calculate the composition [32, 33], for example, -OCH3 on MMA (peak a, δ = 3.5 ppm), -COOH on MMA (peak b, δ = 12.3 ppm), -C6H5 on SM (peak c, δ = 7 ppm), and -OH on HEMA (peak d, δ = 4.8 ppm); -CH2 (peaks e and f, δ = 3.6 ppm and 3.9 ppm) the signal of d6-DMSO (δ = 2.5 ppm) and the signal of H2O (δ = 3.3 ppm). As the reaction continued, the composition ratio of copolymer gradually approached the feed ratio at about 4 h reaction time, and was almost stabilized at reaction time 6 h to 8 h. Samples were taken by batch at different reaction time interval. The composition ratio of copolymer was calculated from the integration areas of the characteristic peaks shown on 1H-NMR. For the reaction at 80 °C, the composition change with reaction time of PMMSH is shown in Table 3.
Fig. 1

Typical proton NMR spectrum for PMMSH

Table 3

Relationship between composition and reaction time of PMMSH(Reaction temperature: 80 °C)

Reaction

Content percentage(%)a

Time (hr)

MMA

MAA

SM

HEMA

feed ratio

57.3

20.6

9.4

12.7

1 h

60.2

16.3

13.1

10.4

2 h

56.2

18.3

13.6

11.9

2.5 h

53.9

20.6

13.5

12.0

4 h

56.1

20.3

11.1

12.5

6 h

58.8

19.3

10.7

11.2

8 h

56.6

20.5

11.2

11.7

9 h

56.7

20.5

11.2

11.6

aThe content percentages are calculated by NMR spectra

The chemical structure of PMMSH(synthesized at 80oC for 2.5 h.) was analyzed by FTIR spectrum shown in Fig. 2. The C = C strecthing peak around 1,600 ~ 1,680 cm-1 of all monomers almost disappeared after polymerization, indicating that the free-radical reaction was well performed. The C = O stretching band of MMA, MAA and HEMA segments in the PMMSH appears at 1,730 cm−1. The peak at 1,159 cm−1 is corresponded to -O-CH3 stretching vibrations of MMA segments [34, 35]. At 3,500–2,500 cm−1, a weak and broad peak is observed, which is caused by the -COOH extension vibration of hydroxyl groups in MAA segments [36]. The O-H stretching peak of HEMA segments around 3,300 cm−1 [37] is weak and appears as a shoulder. For styrene segments, the peaks at 1,495 and 706 cm−1 are assigned to an in-plane and out- plane bending mode of the phenyl ring [38], respectively, and the C-H stretching of the aromatic ring at 3,058 cm−1 [38] is also shown in the spectrum. According to the absence of C = C stretching peak around 1,600 ~ 1,680 cm−1 and the existence of characteristic peaks for each component in PMMSH, it suggested that the free-radical copolymerization of PMMSH was successful.
Fig. 2

IR spectrum of PMMSH

Functional polymer is the main ingredient for the preparation of photoresist and its molecular weight is also one of the important parameters that affect the microlithography performance. If the molecular weight is too large, photoresist will have a slow dissolution rate, which will lengthen the developing period, reduce the yield rate, and even damage the microlithography image of the photoresist. On the other hand, film or membrane will not be formed if the molecular weight is too small. In the current experiment, a fixed amount of initiator(BPO) was used at various reaction temperature. The results of molecular weight obtained are shown in Table 4. As can be seen, the molecular weight decreases with increasing reaction temperature. The change of BPO dissociation rate under different temperature might be the main reason for this phenomenon. In detail, BPO speeds up its disintegration at high temperature, its half-life period is 7.4 h at 70 °C, 1.4 h at 80 °C and 19.8 min at 100 °C, respectively. Hence, the higher the reaction temperature the faster the disintegration of BPO, causes more free radicals in the solution and more polymer chains with free radicals. The free radicals would collide easily to terminate the reaction, resulting in smaller molecular weight.
Table 4

Relationship between PMMSH Reaction Temperature and Molecular Weight

Reaction temperature(°C)

Mwa

Mna

PDIa

70

85962

45240

1.90

80

80843

44361

1.82

90

55143

28425

1.93

100

52530

22711

2.31

120

40385

18866

2.14

aMeasured by GPC

The acid value decides the rate for the developing process. The content of MAA segments in copolymer decides the acid value and makes it soluble in alkaline developing solution. For environmental protection purpose, the process has to avoid the use of organic developing solution. The acid value of copolymer(PMMSH) was measured three times and the average value was 52.58 mg-KOH/g.

Synthesis and characterization of PMMSHgG

The purified PMMSHgG was dissolved in d6-DMSO and 1H-NMR was used to verify its structure and characteristic peaks, as shown in Fig. 3. As can be seen, -OCH3 on MMA (peak a, δ = 3.5 ppm), -COOH on MMA (peak b, δ = 12.3 ppm), -C6H5 on SM (peak c, δ = 7 ppm), -OH on HEMA (peak d, δ = 4.8 ppm); -CH2 on copolymer (peak e, δ = 3.6 ppm and peak f, 3.9 ppm); and = CH2 on GMA (peak g, δ = 6 ppm) all are present in Fig. 3. In addition, the peaks at δ = 2.5 ppm and δ = 3.3 ppm are due to d6-DMSO and H2O, respectively. An additional peak of C = C at δ = 6 ppm appears, proving that GMA indeed grafts with PMMSH to form PMMSHgG. Furthermore, the composition of each component in PMMSHgG was also calculated, the result as 54.2, 19.6, 10.7, 11.2 and 4.3 wt% for PMMA, PMAA, PSM, PMMA and PGMA, respectively.
Fig. 3

Typical proton NMR spectrum for PMMSHgG

Infrared spectrometer was also conducted to ensure the functional group of PMMSHgG as shown in Fig. 4. The C = C stretching peak of GMA segments could be found in spectrum at 1,600 ~ 1,680 cm-1 after introducing the GMA in PMMSH copolymer. It is in consistent with the 1H-NMR result, suggesting that PMMSHgG copolymer is synthesized successfully.
Fig. 4

IR spectrum of PMMSHgG

The PMMSHgGs were prepared by batches at various reaction time and the molecular weights measured by GPC are shown in Table 5. The results show that the changes of molecular weights and polydispersion index are not apparent with reaction time. It might be attributed to the low reactivity for longer copolymer chain.
Table 5

Relationship between reaction time and molecular weight of PMMSHgG(Reaction temperature: 80 °C)

Reaction time(hr)

Mwa

Mna

PDIa

3

102216

51913

1.97

6

100798

49933

2.02

9

107551

52044

2.07

a.Measured by GPC

The changes of PMMSHgG acid value with reaction time are shown in Table 6. The acid value decreases with reaction time and drops to 24.26 mg-KOH/g after 9 h reaction time.
Table 6

Relationship between reaction time and acid value of PMMSHgG(Reaction temperature: 80 °C)

Reaction Time(hr)

Acid value(mg-KOH/g)

1

34.75

2

32.43

3

30.59

4

28.44

5

27.47

6

26.03

7

25.12

8

24.46

9

24.26

Lithographic evaluation of PMMSH-based and PMMSHgG-based Photoresists

The PMMSH or PMMSHgG copolymers, photoinitiator, monomer, solvent, and a few amount of foam control agent were mixed to form the photoresist formulations and the composition is shown in Table 1. The mixture was cast to film and went through microlithography and exposure for different periods under UV light source(with exposure energy of 4.7 mW/cm2 and large wideband) to obtain a negative photoresist with different cross linking degrees and specific curves for sensitivity measurement. The sensitivity of negative photoresist is defined as the energy needed to keep 50 % of the original photoresist thickness in the exposed area. The sensitivity specific curves for both photoresists are illustrated in Fig. 5 and the sensitivity of PMMSH is 4,750 mJ/cm2 and that of PMMSHgG is 480 mJ/cm2, respectively. The sensitivity of PMMSHgG is much better than that of the original PMMSH. After grafted with GMA, the C = C double bonds on GMA segments could provide additional reaction sites for photo reaction with cross-linking agent and therefore to improve the cross linking extent or reduce the required exposure energy. Figure 6 shows the SEM images of PMMSHgG photoresist. It can be seen that the lines are straight and clear after development and the resolving capacity of photoresist is above 10 um. It proves that PMMSHgG photoresist is an effective photoresist.
Fig. 5

Characteristic exposure curve for photoresist of PMMSH and PMMSHgG

Fig. 6

SEM images of (a) PMMSHgG-based photo resist after exposure and development; (b) using a L/S mask

Lithographic evaluation of PMMSHgG-based Photo-imageable Dry-Peelable plastisol on CCL (Copper Clad Laminate)

Current studies and commercial products about photoresist peelable plastisol(photo-imageable dry-peelable plastisol) formed by combining the photoresist and dry-peelable plastisol are rare. Based on this idea, we had tried to mix the photoresist and dry-peelable plastisol and the formula is shown in Table 2. In this plastisol, the PR-450 PVC powder is used as the filler for giving the photoresist peelable function. DBP was the plasticizer and epoxy acrylate oligomer (9,770) is used to enhance the developability with its carboxyl group. Aromatic urethane acrylate oligomer (670A2) is a monomer with six acrylate functional groups. Soybean epoxy could consume HCl formed by thermal decomposition of PVC and avoid the acceleration of PVC decomposition at the same time. After the above ingredients were mixed uniformly, the paste was grounded in a three-roller mill and applied onto a copper plate through screen printing. The morphology of the sample after exposure and development is shown in Fig. 7 and straight and clear patterns are obtained and the resolved line is about 3.17 mil wide.
Fig. 7

Optical micrograph (200x) of PMMSHgG-based photo-imageable dry-peelable plastisol after exposure and development on CCL using a negative mask

Peelable evaluation of PMMSHgG-based photo-imageable Dry-peelable plastisol

The PVC in the formula of photoresist peelable plastisol (Table 2) used are (a) PR-450, (b) PR-1069, and (c) H11/59, respectively. The samples were coated on clean glasses and went through the exposure, heating and baking processes. The peeling test was performed after cooling, and it was justified that there is any scum left. Table 7 shows that PR-450 and PR-1069 are not quite compatible with PMMSHgG, which results in slight lamination in post-baking and scum is found. However, vinyl chloride (89 wt%)/vinyl acetate (11 wt%) copolymer (H11/59) is compatible with PMMSHgG and Fig. 8 shows the complete peeling of H11/59 and no scum is found on the glass. For further confirmation, peeling-off test (The peeling angle is 90o.) of H11/59-based photo-imageable dry-peelable plastisol was also performed and its result is shown in Fig. 9. As can be seen, H11/59 has better compatibility with PMMSHgG than the first two PVC additives. Owing to the elasticity of H11/59-based plastisol, the loading force increased steadily in the initial 20 mm and then kept around 10 gf. The peeling force of 10 gf is a quite lower value. For example, the commercial tape of Scotch® (Transparent Film Tape 600) via the same peeling test showed the peeling force as 170 gf. Since H11/59 containing 11 % vinyl acetate is more compatible with the MMA component in PMMSHgG.
Table 7

Peelable Test of PMMSHgG. The PVC used were (a) PR-450, (b)PR-1069, and (c) H 11/59

 

Polymer

K Value

Peelable test

PR-450a

VCM

65 ± 2

scum

PR-1069a

VCM

78 ± 2

scum

H 11/59b

VCM/VA

59 ± 1

peelable

aPR-450 and PR-1069 were homogeneous PVC taken from Formosa Plastic

bH 11/59 was the copolymer of vinyl chloride and vinyl acetate, taken from WACKER VINNOL

Fig. 8

Peelable evaluation of H 11/59-based photo-imaginable dry-peelable plastisol

Fig. 9

Peeling-off test of H11/59 based photo-imaginable dry-peelable plastisol

Conclusions

In summary, the results of our study show the effectiveness of our approaches to obtain photosensitive prepolymer (PMMSH) via free-radical copolymerization of monomers, including, MMA, MAA, SM and HEMA. Then carboxylic acid groups on MAA are used to graft GMA. Some acid groups are kept as the developing enhancer. Molecular weight of PMMSH decreases with raising reaction temperature. Grafting GMA on PMMSH could form a photosensitive copolymer(PMMSHgG) with good sensitivity. Precision images of both photoresists PMMSH and PMMSHgG could be obtained through exposure and development.

Photosensitive copolymer PMMSHgG and poly(vinyl chloride/vinyl acetate)(H11/59) are compatible, since they both have similar ester moiety. After post-baking, plasitisol (H11/59) was plasticized into tough membrane, which was physically peelable and had no scum left after peeling. In summary, combination of photosensitive copolymer, PMMSHgG and peelable poly(vinyl chloride/vinyl acetate) could fabricate into an innovative photo-imageable dry-peelable temporary protective plastisol successfully.

Notes

Acknowledgement

The authors thank the National Science Council of the Republic of China for the partial financial support of this work under the grant no. of NSC98-2622-E-007-006-CC3.

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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  • Sheng Chang
    • 1
    • 2
  • Jian-He Yang
    • 1
  • Jung-Hsien Chien
    • 1
  • Yu-Der Lee
    • 1
  1. 1.Department of Chemical EngineeringNational Tsing Hua UniversityHsinchuRepublic of China
  2. 2.Greencure Technology CorporationTaoyuanRepublic of China

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